Deformable alloy Zr?Ti?Q?Fe for high-pressure vessels

Nucleation and growth of the γ′(AlAg2) precipitate in Al–Ag(–Cu) alloys

“…The nucleation of a second transformation dislocation in Figure 8(c) would increase the thickness of the hcp region further, and returns the matrix planes to full alignment. This is now structurally identical to the arrangement proposed by Shchegoleva [18], but with nucleation having occurred on a pre-existing stacking fault rather than homogeneously.…”

“…The presence of structures with single, double and triple stacking faults can be explained if thickening of the hcp region can be explained by the passage of single (rather than paired) Shockley partial dislocations. Transformation dislocations were not directly observed; however, the change in stacking on alternate layers (with spacing c(γ ′ ) = 0.46 nm) and the formation of commensurate precipitates for three changes in stacking is consistent with models for the Al(fcc)→γ ′ phase transformation [31] and the formation of strain-accommodated hcp precipitates [18].…”

“…It has been proposed that the nucleation of a hcp phase in a fcc matrix could be accomplished homogeneously in an analogous manner through the formation of a "self-accommodating" unit in which transformation dislocations in each layer were balanced by those in adjacent layers [18]. This requires a minimum thickness of seven atomic close-packed layers (3×c(AlAg 2 )) to allow the outer-most atomic planes of the precipitate to maintain coherence with the matrix.…”